1. Field of the Invention
This invention relates to new and improved apparatus and methods for forming corrugations in metal heat exchange tubing.
2. Brief Description of the Prior Art
Finned heat exchange tubing is well known in the art for use in radiators, heat exchangers, refrigeration condensors, etc. Many types of apparatus and methods are known for the application of heat exchange fins to heat exchanger tubing.
It is also well known to form heat exchange fins integrally from the wall of heat exchange tubing members. It is also known to corrugate heat exchange tubing into longitudinally extending or circumferentially or helically extending corrugations to provide an increased surface area for heat exchange similar to the effect produced by external fins on the tubing. The production of helical corrugations and tubing, however, has in the past required the use of an internal mandrel and an external corrugation die cooperable therewith to form the desired corrugations. Such equipment has limited the length of helically corrugated tubing to the length of mandrel used in the corrugation operation. This has not been a practical method for continuous corrugation of very long thin walled heat exchange tubing.
Benson U.S. Pat. No. 2,954,212 discloses apparatus for extrusion of metal tubing with helical fins formed integrally thereon.
Slade U.S. Pat. No. 3,008,187 discloses an extrusion die for extruding thermoplastics having helical corrugations for orienting the plastic material in different directions.
Atkin U.S. Pat. No. 3,267,712 discloses an extrusion die for extruding tubing with longitudinally extending fins thereon.
Brothers U.S. Pat. No. 4,159,739 discloses a method and apparatus for forming heat exchange fins integrally from the material of heat exchange tubing.
Ford U.S. Pat. No. 3,850,227 discloses a helically corrugated heat exchange tubing and makes reference in his specification to other types of tubing and to apparatus used for forming such tubing.
Regner U.S. Pat. No. 3,988,804 discloses the use of a rotating die having helical internal fins for forming thin walled tubular cellophane film into a pleated or shirred form having helically formed pleats.
Zifferer and Shepherd U.S. Pat. No. 4,377,083 (commonly assigned) shows and a corrugating die similar to the present invention. In the manufacture of corrugating dies in accordance with that invention, it was found that the die teeth have a much smaller clearance between the inner end portions of adjacent teeth as the number of die teeth is increased. As a result of this discovery, it has been necessary to modify the die substantially when constructed with more than 4 or 5 teeth.
The prior art cited in the prosecution of U.S. Pat. No. 4,377,083 is relevant to this application but does not suggest the invention disclosed and claimed herein.